Testing a new autopilot in instrument conditions

David Megginson, the blogger behind the Land and Hold Short blog, has recently written a post about testing his new autopilot in instrument conditions. David began his post by pointing out that his new autopilot has four modes (without altitude support) as currently configured and then he went into detail about how each of the modes worked for him during his initial test flights:

• Stabilization Mode (ST). This mode keeps the wings level so that a pilot can fly a hyper-stabilized plane like in Microsoft Flight Simulator. David noted that this mode is useless to him and he has only used it during initial tests or pre-flight checks. He also added that if he wants to  steer the aircraft using the autopilot, it makes more sense to twirl the heading bug on the heading indicator and then to have the autopilot follow it.
• Heading Mode (HD). This mode keeps the aircraft on a specific heading. David mentioned that he tried to not touch the yoke when it was in HD mode and then correct any altitude deviations using the trim. However, he also added that despite working hard to damp out oscillations, it was still be a challenge for him while flying in turbulence.
• VOR-Tracking Mode or TRK (LO). This mode keeps the VOR CDI centered using a low-pass filter. However, David pointed out that the problem with this mode is that the VOR needles will scallop back and forth considerably – meaning the aircraft will still gently weave during a flight. Hence and in IMC, he found the heading mode to be much more effective.
• Localizer-tracking Mode or TRK (HI): This mode keeps the VOR CDI centered with more-aggressive corrections. However, David wrote that he tried this mode on an approach to an airport but from 10 miles back, it did not seem like it was doing a good job as sometimes it was allowing nearly a half deflection on the CDI. Hence, he disengaged the autopilot before flying too low and flew the remainder of the approach by hand.

Nevertheless, David concluded that having an autopilot makes a huge difference in the level of fatigue he has after a flight – especially in flying conditions that require constant attention. Furthermore, he added that the autopilot helps him relax more so that he can study approach plates better and pay more attention to the engine gauges. In other words and for David, the autopilot was worth the investment.